1. Field of the Invention
The present invention relates to a coupling device. More particularly, the present invention relates to a power coupling device for transmitting power between a driving unit of an organic photoconductor (OPC) of an electrophotographic image forming apparatus, and an image forming apparatus having the same.
2. Description of the Related Art
Electrophotographic image forming apparatuses include a photocopier, a printer, a facsimile and a word processor. In such image forming apparatuses, an electrostatic latent image is formed by exposing a photoconductive medium evenly electrified by an electrifying unit to a laser for forming an image. The electrostatic latent image is developed into a toner image by a developing unit having a toner. The toner image is transferred onto a recording medium by a transfer unit, thereby forming an image.
In the case of a color image forming apparatus, electrostatic latent images are formed on a plurality of photoconductive mediums for different colors, such as magenta, cyan, yellow and black, and developed by the respectively different colors of toner. The toner images of different colors are overlapped and transferred onto an intermediate recording medium, such as an intermediate transfer belt. The transferred intermediate toner images are transferred onto a final recording medium, thereby forming a color image on the final recording medium.
Here, since the intermediate transfer belt or the photoconductive mediums of different colors are expendables that have limited lifespans, they need to be replaced at the end of the expendable's lifespans.
Recently, image forming apparatuses have been provided with a process cartridge removably mounted in a main body thereof, wherein expendables such as the photoconductive medium, the electrifying unit, the developing unit and a cleaning unit are all integrated as one part. The process cartridge is removably mounted in the image forming apparatus by a driving unit for supplying power and a coupling device.
FIG. 1 schematically shows a conventional power coupling device of an image forming apparatus. The conventional power coupling device comprises a driving coupler 10 and a driven coupler 20.
The driving coupler 10 is rotatably mounted in a driving unit 1 in the image forming apparatus. The driving coupler 10 comprises a coupling recess 11 depressed by a certain depth and having a non-circular section, and a positioning recess 12 formed at one side of the coupling recess 11.
The driven coupler 20 comprises a coupling protrusion 21 fixed at one side of a photoconductive drum 2 and protruding by a certain height to correspond to the coupling recess 11, and a positioning protrusion 22.
Although schematically shown in the drawings, the driving coupler 10 and the driven coupler 20 are provided in different colors, and the power of the driving unit 1 can be transmitted to the respective photoconductive mediums 2 by coupling of the driving coupler 10 and the driven coupler 20, thereby rotating the photoconductive medium 2.
In the above-structured image forming apparatus, in order to implement color registration of high precision by reducing image offset incurred by errors such as a manufacturing error, a forming error and an assembly error, a method is used, which regulates the eccentricities of the respective photoconductive mediums 2 of different colors.
In other words, peak eccentric positions are checked, such as where radiuses of the respective photoconductive mediums 2 are the greatest, and the driven coupler 20 is fixed to the respective photoconductive mediums 2 in a manner that the positioning protrusion 22 of the driven coupler 20, for example, is located at the peak eccentric position, such that the photoconductive mediums 2 are coupled with the driving unit at the same phase. In this case, although the offset occurs with respect to the standard, the offset among the respective colors decreases. Therefore, the visual color registration seems insignificant.
However, according to the conventional method as described above, it is hard to select and group the photoconductive mediums 2 having the same peak eccentric positions because the peak eccentric positions of the photoconductive mediums 2 may change when fixing the driven coupler 20 to the photoconductive mediums 2 after measuring the peak eccentric positions of the respective photoconductive mediums 2.
Furthermore, using the conventional method, the color registration in consideration of the manufacturing error and the forming error can be compensated, however, the assembly error (for example, an error of a distance between the centers of the photoconductive mediums) may not be considered in compensating the color registration. Therefore, improvement in image quality is limited.
There are other ways for regulating the peak eccentric positions of the photoconductive mediums 2: one is using a driving system and a sensor clutch; and the other is using a plurality of motors corresponding to the number of the photoconductive mediums. In the former way, a certain position of the photoconductive medium is marked to be recognized as a sensor, such that the peak eccentric positions of the respective photoconductive mediums are uniformly driven. In the latter way, the respective photoconductive mediums are separately driven by the plurality of motors without an intermediate clutch.
However, the conventional methods as described above require an electronic controller or a controlling algorithm with a complicated structure. Therefore, they are not cost-effective or time-effective.